Lead Dress: OD V2a Grid wire

[Charlie Wilson]

Martin, what about phase cancelation. Would lower frequencies have a wider field around the wires the higher ones?
CW

[martin manning]

Martin, what about phase cancelation. Would lower frequencies have a wider field around the wires the higher ones?

It would be the opposite, with the reactance of the lead-to-lead capacitance being lower at higher frequencies. Inductive coupling has been mentioned several times, but the plate current is very small, so that should be minimal.

[talbany]

I played with this a bit more last night. What I am hearing is the closer the wires, the more bass and mids are attenuated until they are touching and then its shrill top end. With my amp, if I get a sound I like at a low volume with a singing top end and then turn the amp up the OD gets hard and bright and looses the sing on the top end. If I move the wire away from each other, the OD sounds a bit dark and dull at a low volume but as I turn the amp up it fattens ups the sound and the top end sing comes in. This is with a rather bright Strat. I believe Dumble flew the wire as he did in #124 to fatten up the sound of a Strat which is what the amp was tweeked for. I will note that I have the same wire in my amp as Martin. There have been many "My amp OD is too bright" posts over the years and I can't help but wonder how many amps could have been made to sound better by moving a wire instead of HF tapers, higher capacitance coax, etc.
CW

i already had the low plate Classic out of the cab and I hear basically the same hollow low end & shrill or gritty on top (wire tied) Plate and grid
(Couldn't crank it to much wife is home)

20210511_141522.jpg

What I am hearing is the closer the wires, the more bass and mids are attenuated until they are touching and then its shrill top end.

I also noticed some slight loss of sustain (sing??). It was noticeable but would't call it horrendous or not playable.
Teflon PVC from Jim @ Ampex.
Tony

[ChopSauce]

Martin, it would be really interesting to see if you get the same results on the breadboard using solid core instead of topcoat.

It's not something I would rely on but I remember having been taught that solide core wire is more prone to induction.

[Audiodog]

My amps are Teflon. Could be the jacket shielding against the induction when touching.

This is a bizarre thread for me as the effect is so extreme that the amps effected were virtually unusable in OD mode.

Maybe the wire brand and type matters?

The amp I tested has 22 ga. UL1015 600V PVC stranded topcoat wire. Nothing special.

It's been Eons since I revisited this so went back over some older notes. Again!.. I hope this helps!

Source: "Lead Dress in Tube Amps," R. G. Keen, 2005 http://www.geofex.com/article_folders/l ... e_amps.htm Good reading, like all of R.G.'s stuff.

[Charlie Wilson]

I played with this a bit more last night. What I am hearing is the closer the wires, the more bass and mids are attenuated until they are touching and then its shrill top end. With my amp, if I get a sound I like at a low volume with a singing top end and then turn the amp up the OD gets hard and bright and looses the sing on the top end. If I move the wire away from each other, the OD sounds a bit dark and dull at a low volume but as I turn the amp up it fattens ups the sound and the top end sing comes in. This is with a rather bright Strat. I believe Dumble flew the wire as he did in #124 to fatten up the sound of a Strat which is what the amp was tweeked for. I will note that I have the same wire in my amp as Martin. There have been many "My amp OD is too bright" posts over the years and I can't help but wonder how many amps could have been made to sound better by moving a wire instead of HF tapers, higher capacitance coax, etc.
CW

i already had the low plate Classic out of the cab and I hear basically the same hollow low end & shrill or gritty on top (wire tied) Plate and grid
(Couldn't crank it to much wife is home)
20210511_141522.jpg

What I am hearing is the closer the wires, the more bass and mids are attenuated until they are touching and then its shrill top end.

I also noticed some slight loss of sustain (sing??). It was noticeable but would't call it horrendous or not playable.
Teflon PVC from Jim @ Ampex.
Tony

Tony, I think you told me that you like your trimmer set fairly low. I set mine at about 40k to ground and the effect is very noticeable.
CW

[ijedouglas]

I played with this a bit more last night. What I am hearing is the closer the wires, the more bass and mids are attenuated until they are touching and then its shrill top end. With my amp, if I get a sound I like at a low volume with a singing top end and then turn the amp up the OD gets hard and bright and looses the sing on the top end. If I move the wire away from each other, the OD sounds a bit dark and dull at a low volume but as I turn the amp up it fattens ups the sound and the top end sing comes in. This is with a rather bright Strat. I believe Dumble flew the wire as he did in #124 to fatten up the sound of a Strat which is what the amp was tweeked for. I will note that I have the same wire in my amp as Martin. There have been many "My amp OD is too bright" posts over the years and I can't help but wonder how many amps could have been made to sound better by moving a wire instead of HF tapers, higher capacitance coax, etc.
CW

i already had the low plate Classic out of the cab and I hear basically the same hollow low end & shrill or gritty on top (wire tied) Plate and grid
(Couldn't crank it to much wife is home)
20210511_141522.jpg

What I am hearing is the closer the wires, the more bass and mids are attenuated until they are touching and then its shrill top end.

I also noticed some slight loss of sustain (sing??). It was noticeable but would't call it horrendous or not playable.
Teflon PVC from Jim @ Ampex.
Tony

Pretty much the same as my experience. Fills out the bass and mids and increases sustain. The effect is more pronounced when I get to 3.5-4 on the master (pretty loud)

[talbany]

Tony, I think you told me that you like your trimmer set fairly low. I set mine at about 40k to ground and the effect is very noticeable.
CW

C.W
I set my trimmer at 27K fairly low. My L.P.C has 25uF on V1a & B and a .047 V1b coupler. So I have plenty of low end on that amp. The OD side is slightly darker than the Clean channel too so it's not a bright amp by any stretch..Really I didn't get to spend a lot of time with it since my wife just got out of hospital. So I just wanted to confirm what you were hearing ..Perhaps when I get more time I can give you a more detailed response. So for now i am sticking with I noticed it. Either way I recommend keeping those wires apart.

BTW.For those who think the amp is unplayable like that. then it's "un-playable"

Tony

[Audiodog]

No need for sarcasm…. The amps were indeed unplayable. Pumping volume makes for unplayable ( the Ceriatone). The other one had a wonky bass control and horrible shrillness on top. Guy spent hundreds sending the amp here because it was unplayable. Really bad sounding. Either I am an idiot or a liar. I am neither. I suspect the type of wires matter, as does the tube type, volume level, and high plate/low plate. It can be really bad on some amps. We will find out what the California guy thinks when he gets his amp on Wednesday.

BTW.For those who think the amp is unplayable like that. then it's "un-playable"

Tony

[ChopSauce]

I'm not sure there was any sarcasm at all in Tony's post. He (also) seems to all agree with you - as far as my understanding of english allows.

Martin could not reproduce the problem on his bench. That does not mean anything more than that. He is right to doubt. It is his duty even, I think.

[Charlie Wilson]

Scott, I, as stated before, I am able to hear a not subtle difference in moving that wire and even at a bit of a distance(more that 1/2 inch). I appreciate the scientific approach to scoping and simulating but if several people hear a similar effect than there is the possibility that we simply don't know why it behaves that way. I just find the idea that if we don't have a technical reason for why something sounds the way it does than it doesn't exist vibe a bit, well, irritating. I have in good faith, sent NOS resistors to people and read through dozens of posts of people going through considerable effort trying to disprove that they sound any different. I am starting to see why certain pro builders are starting to keep their sonic secrets off the forum.
CW

[martin manning]

The amps were indeed unplayable. Pumping volume makes for unplayable ( the Ceriatone). The other one had a wonky bass control and horrible shrillness on top. Guy spent hundreds sending the amp here because it was unplayable. Really bad sounding...

This is what I got from your description earlier, something really awful, not the kind of thing that is only perceptible by a chosen few.

I suspect the type of wires matter, as does the tube type, volume level, and high plate/low plate.

Wire type? I don't think so, but the contact/no contact is really odd.
I have to believe the problem is oscillation, and that means there is positive feedback coming from somewhere, and it's not likely to be the out of phase plate lead. A prime suspect would be the OD2 stage, and I can see where moving that wire might bring sonic differences due to its being closer to or farther from breaking into oscillation. The high plate configuration adds a little gain, but in either case the HF is rolled-off substantially by the snubber. With a 270p plate-to-cathode the corner is way down, around 6kHz.

I just find the idea that if we don't have a technical reason for why something sounds the way it does than it doesn't exist vibe a bit, well, irritating.

Sorry, I guess one man's irritation is another man's enlightenment. ;^)

[pompeiisneaks]

I could add one other bit of information.

I had my ODS clone built on the LuigiRetroCustom boards have horrid oscillations based on lead dress. I tested this by connecting some copper plate I had to ground and then with insulated pliers put it between V1 and V2 and the oscillation and horrid sounds disappeared. At that point I'd discovered that wiring V1b as the first input and then having that right next to V2 meant that the od channel's signal bled back into the leads of V1b and caused horrid noise. I could see careful positioning of these wires could definitely improve/worsen this.

I just swapped V1a and V1b wires and the problem went away as the second gain stage had enough gain to reject noise from the V2 tube.

Not sure if related, but possible?

~Phil

[ayan]

Wire type? I don't think so, but the contact/no contact is really odd.
I have to believe the problem is oscillation, and that means there is positive feedback coming from somewhere, and it's not likely to be the out of phase plate lead. A prime suspect would be the OD2 stage, and I can see where moving that wire might bring sonic differences due to its being closer to or farther from breaking into oscillation. The high plate configuration adds a little gain, but in either case the HF is rolled-off substantially by the snubber. With a 270p plate-to-cathode the corner is way down, around 6kHz.

Without experimenting with the placement of the V2A grid wire, I would agree with the statement above. From what I recall, I never ran into oscillation issues with the ODS layout -- but I had my share of trouble with oscillations building a pseudo ODS (+ reverb) in a Fender Deluxe Reverb chassis/board. But, I am curious and will mess with the V2A grid wire location in one of my amps and see what I find out.

[norburybrook]

can't someone with one of these amps that responds this way just stick a microphone in front of the amp and record it. If you're only moving a wire it's a super easy thing to do then we'll all hear it or you can do a spectro analysis /FFT of whatever and see where the differences are. Just set up a looper so it takes the player out of the equation, that was my mistake in my resistor test I just played before and after and that put a huge variable in there, a looper removes that.

I'm busy in the studio with projects and about to get married so I don't have time to do it but if no one else does i shall in June when the decks are clearer.


M

p.s. I think Tony meant that when the player thinks an amp is unplayable for whatever reason the it becomes unplayable to him/her as no one like to play an amp they don't like the sound of.